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# Derivative of xlnx = 1? watch

1. Hi there,

Answer book says xlnx differentiates to 1 + lnx - how did they get to this? I got y= xlnx so dy/dx = x/x = 1
2. let u = lnx differentiates to 1/x
let v = x differentiates to 1

d(uv)/dx = (du/dx)*v + (dv/dx)*u (product rule)
= x/x + lnx = 1 + lnx
3. (Original post by Retropmot)
let u = lnx differentiates to 1/x
let v = x differentiates to 1

d(uv)/dx = (du/dx)*v + (dv/dx)*u (chain rule)
= x/x + lnx = 1 + lnx
Product rule, you mean.
4. (Original post by Craver)
Hi there,

Answer book says xlnx differentiates to 1 + lnx - how did they get to this? I got y= xlnx so dy/dx = x/x = 1
It couldnt possible = 1 since the integral of 1 with respext to x is x+c, which =/=xlnx

As above, product rule

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Updated: April 11, 2006
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